We have been studying the efficacy of local injections of botulinum toxin for the treatment of different types of focal dystonias. Botulinum toxin injected in small doses directly into muscle, binds to and inactivates the neuromuscular junction. Dystonic contraction is decreased and function improves Treatment is well-tolerated with minimal side effects. We have also used botulinum toxin to study the physiology of focal dystonias. A double-blind trial of botulinum toxin for hand dystonia (e.g. writer's cramp and musician's cramp) showed a significant improvement in function following injection of active botulinum toxin compared to placebo. Open-label studies have shown that 84% of patients have at least short- term benefit. Longer follow-up shows that approximately 50% of patients have persistent benefit. Women with nonlocalized symptoms or dystonic cramp who require less frequent injections were especially likely to continue treatment. Botulinum toxin injection is well-tolerated. Botulinum toxin injections have been similarly effective in our patients with other types of dystonia. Twelve patients with tremor have been treated to date. All of the patients with torticollis and head tremor who received at least 3 injections had at least mild improvement. 50% of the patients with arm tremor had substantial improvement. One patient noted increased tremor after injection. We are conducting a phase I-II trial of botulinum toxin type F to see if this will benefit patients who have lost response to type A. Type F appears to have similar efficacy and side effects to type A, although the duration of action is slightly less.